Influence of chlorine on co-processing of hazardous wastes in brick kilns

Abstract

Brick kiln co-treatment is a novel industrial hazardous wastes (IHWs) utilization process. However, the effects of chlorine (Cl) in wastes on heavy metals (HMs) during this process are overlooked. This study investigated the stabilization/solidification (S/S) and volatilization, as well as long and short-term leaching, of HMs in Cl-containing bricks. The results indicated enhanced formations of stable mineral phases (NiFe2O4, Ni2SiO4, Cd3Al2Si3O12, CdSiO3, FeCr2O4, Cr2O3, CuFe2O4, and CuAl2O4) in bricks at a low sintering temperature (800 °C) due to the affinity between Cl and HMs. By comparing HM concentrations before and after sintering in bricks, the study observed that Cl's presence significantly elevated the volatilization rates for Cd and Cu by 30.8% and 14.2%, respectively. In contrast, the effect on volatilization for Ni and Cr was not significant. Additionally, utilizing the NEN 7375 method, the cumulative leaching rates of Ni, Cd, Cr, and Cu over a 64-day experiment under extremely acidic conditions were 0.22%, 7.18%, 0.01%, and 1.46%, respectively. Similarly, higher short-term leaching rates of Cd (4.03%) and Cu (5.73%) than those of Ni (0.94%) and Cr (0.08%) were observed. This finding might be attributed to the lower stability of the Cd and Cu solid phases under acidic environments compared to those of Ni and Cr. Surface wash-off, dissolution, and diffusion were the processes governing HM leaching from bricks. The 10-year projections revealed a minimal release of HMs during future extended leaching, implying the successful S/S of HMs. This study provides a reference for assessing the environmental impacts of brick kiln co-processing of Cl-containing IHWs.